Hydrogen assisted undoped silicon oxide deposition process for HDP-CVD

ABSTRACT

A substrate processing apparatus comprising a substrate processing chamber, a gas distribution system operatively coupled to the chamber, a high density plasma power source, a controller operatively coupled to the gas distribution system and the high density plasma power source and a memory coupled to the controller. The memory includes computer instructions embodied in a computer-readable format. The computer instructions comprise (i) instructions that control the gas distribution system to flow a process gas comprising a silane gas, an oxygen-containing source, an inert gas and a hydrogen-containing source that is either molecular hydrogen or a hydride gas that does not include silicon, boron or phosphorus and (ii) instructions that control the high density plasma source to form a plasma having an ion density of at least 1×10 11  ions/cm 3  from the process gas to deposit the silicon oxide layer over the substrate.

CROSS-REFERENCES TO RELATED APPLICATIONS

[0001] This application is a division of U.S. application Ser. No.09/854,406, filed May 11, 2001, entitled “Hydrogen Assisted UndopedSilicon Oxide Deposition Process For HDP-CVD,” having Zhengquan Tan,Dongqing Li, Walter Zygmunt and Tetsuya Ishikawa listed as coinventors.The 09/854,406 application is assigned to Applied Materials, Inc., theassignee of the present invention and is hereby incorporated byreference.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to the manufacture of integratedcircuits. More specifically, the invention relates to an improved methodof depositing silicon oxide layers for use as insulation layers in suchintegrated circuits.

[0003] One of the primary steps in the fabrication of modernsemiconductor devices is the formation of a film, such as a siliconoxide, on a semiconductor substrate. Silicon oxide is widely used as aninsulating layer in the manufacture of semiconductor devices. As is wellknown, a silicon oxide film can be deposited by thermal chemical vapordeposition (CVD) or a plasma-enhanced chemical vapor deposition (PECVD)processes. In a conventional thermal CVD process, reactive gases aresupplied to the substrate surface where heat-induced chemical reactions(homogeneous or heterogeneous) take place to produce a desired film. Ina conventional plasma process, a controlled plasma is formed todecompose and/or energize reactive species to produce the desired film.

[0004] Semiconductor device geometries have dramatically decreased insize since such devices were first introduced several decades ago.Smaller feature sizes have resulted in the presence of increased aspectratio gaps for some applications, for example, between adjacentconductive lines or in etched trenches. The aspect ratio of a gap isdefined by the ratio of the gap's height or depth to its width. Thesespaces are difficult to fill using conventional CVD methods. A film'sability to completely fill such gaps is referred to as the film's“gap-filling” ability. Silicon oxide is one type of insulation film thatis commonly used to fill the gaps in intermetal dielectric (IMD)applications, premetal dielectric (PMD) applications and shallow trenchisolation (STI) applications among others. Such a silicon oxide film isoften referred to as a gap-fill film or a gap-fill layer.

[0005] Some integrated circuit manufacturers have turned to the use ofhigh density plasma CVD (HDP-CVD) systems to deposit silicon oxidegap-fill layers. HDP-CVD systems form a plasma that is approximately twoorders of magnitude or greater than the density of a standard,capacitively-coupled plasma CVD system. Examples of HDP-CVD systemsinclude inductively-coupled plasma systems and electron cyclotronresonance (ECR) plasma systems among others. HDP-CVD systems generallyoperate at lower pressure ranges than low density plasma systems. Thelow chamber pressure employed in HDP-CVD systems provides active specieshaving a long mean-free-path and reduced angular distribution. Thesefactors, in combination with the plasma's density, contribute to asignificant number of constituents from the plasma reaching even thedeepest portions of closely spaced gaps, providing a film with improvedgap-fill capabilities as compared to films deposited in a low densityplasma CVD system.

[0006] Another factor that allows films deposited by HDP-CVD techniquesto have improved gap-fill characteristics as compared to films depositedby other CVD techniques is the occurrence of sputtering, promoted by theplasma's high density, simultaneous with film deposition. The sputteringelement of HDP deposition slows deposition on certain features, such asthe corners of raised surfaces, thereby contributing to the increasedgap-fill ability of HDP deposited films. Some HDP-CVD systems introduceargon or a similar heavy inert gas to further promote the sputteringeffect. These HDP-CVD systems typically employ an electrode within thesubstrate support pedestal that enables the creation of an electricfield to bias the plasma toward the substrate. The electric field can beapplied throughout the HDP deposition process to further promotesputtering and provide better gap-fill characteristics for a given film.One HDP-CVD process commonly used to deposit a silicon oxide film formsa plasma from a process gas that includes silane (SiH₄), molecularoxygen (O₂) and argon (Ar). This silicon oxide film has improvedgap-fill characteristics as opposed to some silicon oxide filmsdeposited by other non-HDP-CVD plasma techniques and is useful for avariety of applications. Despite the improvement in gap-fill capabilityprovided by HDP-CVD systems and the relatively good gap-fillcharacteristics of HDP-CVD silicon oxide films in particular, thedevelopment of film deposition techniques that enable the deposition ofsilicon oxide layers having even further improved gap-fillcharacteristics are desirable. Such improved silicon oxide filmdeposition are particularly desirable in light of the aggressivegap-fill challenges presented by integrated circuit designs employingminimum feature sizes of 0.18 microns and less.

SUMMARY OF THE INVENTION

[0007] Embodiments of the present invention pertain to an improvedmethod of depositing silicon oxide films using HDP-CVD depositiontechniques. These embodiments enable improved gap-fill capabilities ascompared to HDP-CVD silicon oxide deposition techniques that do notemploy the method of the present invention and the embodiments areuseful for the manufacture of integrated circuits having minimum featuresizes of 0.18 microns or less.

[0008] In one embodiment, the present invention forms an undoped siliconoxide layer (USG) over a substrate disposed in a high density plasmasubstrate processing chamber. The silicon oxide layer is formed byflowing a process gas into the substrate processing chamber and forminga high density plasma (i.e., a plasma having an ion density of at least1×10¹¹ ions/cm³) from the process gas to deposit said silicon oxidelayer over said substrate. The process gas includes a silane gas, anoxygen-containing source, an inert gas and a hydrogen-containing sourcethat is selected from the group of H₂, H₂O, NH₃, CH₄, C₂H₆, or a hydridegas that does not include silicon, boron or phosphorus. The depositedsilicon oxide layer has a hydrogen content of less than or equal to 2atomic percent.

[0009] In another embodiment, the present invention forms an undopedsilicon oxide layer (USG) from a process gas consisting of SiH₄, O₂, Arand H₂. The flow rate ratio of O₂ to the combined flow of SiH₄ and H₂ inthe process gas is between 1.6-2.5:1 inclusive and the flow rate ratioof H₂ to SiH₄ is between 0.5-2.0:1 inclusive. The process gas is flowedinto the substrate processing chamber and a high density plasma isformed from the process gas to deposit the silicon oxide layer over thesubstrate. The deposited silicon oxide layer has a dielectric constantof between 4.0 and 4.2 and contains less than or equal to 2 atomicpercent hydrogen.

[0010] These and other embodiments of the present invention, as well asits advantages and features are described in more detail in conjunctionwith the text below and attached figures.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1A is a simplified diagram of one embodiment of a highdensity chemical vapor deposition system according to the presentinvention;

[0012]FIG. 1B is a simplified cross section of a gas ring that may beused in conjunction with the exemplary CVD processing chamber of FIG.1A;

[0013]FIG. 1C is a simplified diagram of a monitor and light pen thatmay be used in conjunction with the exemplary CVD processing chamber ofFIG. 1A;

[0014]FIG. 1D is a flow chart of an exemplary process control computerprogram product used to control the exemplary CVD processing chamber ofFIG. 1A;

[0015]FIG. 2 is a flowchart illustrating one embodiment of the method ofthe present invention;

[0016] FIGS. 3A-3C are simplified cross-sectional views of a siliconoxide film at different stages of deposition within a narrow width, highaspect ratio gap according to a prior art silicon oxide depositionprocess;

[0017] FIGS. 4A-4C are simplified cross-sectional views of a siliconoxide film, deposited according to an embodiment of the presentinvention, at different stages of deposition within the same narrowwidth, high aspect ratio gap shown in FIGS. 4A-4C;

[0018]FIGS. 5A and 5B are a simplified cross-sectional view of thegap-fill capability of a silicon oxide film deposited according to apreviously known HDP-CVD process; and

[0019]FIGS. 6A and 6B are a simplified cross-sectional view of thegap-fill capability of a silicon oxide film deposited, according to anembodiment of the present invention, over the same gaps as those shownin FIGS. 5A and 5B.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

[0020] I. Introduction

[0021] Embodiments of the present invention deposit an improved siliconoxide layer using high density plasma CVD techniques. The depositedlayer has improved gap-fill capabilities as compared to some prior artsilicon oxide deposition techniques. Films deposited by the method ofthe present invention are suitable for use in the fabrication ofintegrated circuits having feature sizes of 0.18 microns or less.

[0022] Embodiments of the present invention can be implemented using avariety of high density plasma CVD substrate processing chambersincluding chambers in which a plasma is formed by the application of RFenergy to a coil that at least partially surrounds a portion of thechamber and chambers that use ECR plasma formation techniques. Anexample of an inductively-coupled HDP-CVD chamber in which embodimentsof the method of the present invention can be practiced is set forthbelow.

[0023] II. Exemplary Substrate Processing System

[0024]FIG. 1A illustrates one embodiment of a high density plasmachemical vapor deposition (HDP-CVD) system 10 in which a dielectriclayer according to the present invention can be deposited. System 10includes a chamber 13, a vacuum system 70, a source plasma system 80A, abias plasma system 80B, a gas delivery system 33, and a remote plasmacleaning system 50.

[0025] The upper portion of chamber 13 includes a dome 14, which is madeof a ceramic dielectric material, such as aluminum oxide or aluminumnitride. Dome 14 defines an upper boundary of a plasma processing region16. Plasma processing region 16 is bounded on the bottom by the uppersurface of a substrate 17 and a substrate support 18.

[0026] A heater plate 23 and a cold plate 24 surmount, and are thermallycoupled to, dome 14. Heater plate 23 and cold plate 24 allow control ofthe dome temperature to within about ±10 C over a range of about 100° C.to 200° C. This allows optimizing the dome temperature for the variousprocesses. For example, it may be desirable to maintain the dome at ahigher temperature for cleaning or etching processes than for depositionprocesses. Accurate control of the dome temperature also reduces theflake or particle counts in the chamber and improves adhesion betweenthe deposited layer and the substrate.

[0027] Generally, exposure to the plasma heats a substrate positioned onsubstrate support 18. Substrate support 18 includes inner and outerpassages (not shown) that can deliver a heat transfer gas (sometimesreferred to as a backside cooling gas) to the backside of the substrate.

[0028] The lower portion of chamber 13 includes a body member 22, whichjoins the chamber to the vacuum system. A base portion 21 of substratesupport 18 is mounted on, and forms a continuous inner surface with,body member 22. Substrates are transferred into and out of chamber 13 bya robot blade (not shown) through an insertion/removal opening (notshown) in the side of chamber 13. Lift pins (not shown) are raised andthen lowered under the control of a motor (also not shown) to move thesubstrate from the robot blade at an upper loading position 57 to alower processing position 56 in which the substrate is placed on asubstrate receiving portion 19 of substrate support 18. Substratereceiving portion 19 includes an electrostatic chuck 20 that secures thesubstrate to substrate support 18 during substrate processing. In apreferred embodiment, substrate support 18 is made from an aluminumoxide or aluminum ceramic material.

[0029] Vacuum system 70 includes throttle body 25, which housestwin-blade throttle valve 26 and is attached to gate valve 27 andturbo-molecular pump 28. It should be noted that throttle body 25 offersminimum obstruction to gas flow, and allows symmetric pumping, asdescribed in co-pending, co-assigned U.S. patent application Ser. No.08/574,839, filed Dec. 12, 1995, and which is incorporated herein byreference. Gate valve 27 can isolate pump 28 from throttle body 25, andcan also control chamber pressure by restricting the exhaust flowcapacity when throttle valve 26 is fully open. The arrangement of thethrottle valve, gate valve, and turbo-molecular pump allow accurate andstable control of chamber pressures from between about 1 mTorr to about2 Torr.

[0030] The source plasma system 80A includes a top coil 29 and side coil30, mounted on dome 14. A symmetrical ground shield (not shown) reduceselectrical coupling between the coils. Top coil 29 is powered by topsource RF (SRF) generator 31A, whereas side coil 30 is powered by sideSRF generator 31B, allowing independent power levels and frequencies ofoperation for each coil. This dual coil system allows control of theradial ion density in chamber 13, thereby improving plasma uniformity.Side coil 30 and top coil 29 are typically inductively driven, whichdoes not require a complimentary electrode. In a specific embodiment,the top source RF generator 31A provides up to 2,500 watts of RF powerat nominally 2 MHz and the side source RF generator 31B provides up to5,000 watts of RF power at nominally 2 MHz. The operating frequencies ofthe top and side RF generators may be offset from the nominal operatingfrequency (e.g. to 1.7-1.9 MHz and 1.9-2.1 MHz, respectively) to improveplasma-generation efficiency.

[0031] A bias plasma system 80B includes a bias RF (BRF) generator 31Cand a bias matching network 32C. The bias plasma system 80B capacitivelycouples substrate portion 17 to body member 22, which act ascomplimentary electrodes. The bias plasma system 80B serves to enhancethe transport of plasma species (e.g., ions) created by the sourceplasma system 80A to the surface of the substrate. In a specificembodiment, bias RF generator provides up to 5,000 watts of RF power at13.56 MHz.

[0032] RF generators 31A and 31B include digitally-controlledsynthesizers and operate over a frequency range between about 1.8 toabout 2.1 MHz. Each generator includes an RF control circuit (not shown)that measures reflected power from the chamber and coil back to thegenerator and adjusts the frequency of operation to obtain the lowestreflected power, as understood by a person of ordinary skill in the art.RF generators are typically designed to operate into a load with acharacteristic impedance of 50 ohms. RF power may be reflected fromloads that have a different characteristic impedance than the generator.This can reduce power transferred to the load. Additionally, powerreflected from the load back to the generator may overload and damagethe generator. Because the impedance of a plasma may range from lessthan 5 ohms to over 900 ohms, depending on the plasma ion density, amongother factors, and because reflected power may be a function offrequency, adjusting the generator frequency according to the reflectedpower increases the power transferred from the RF generator to theplasma and protects the generator. Another way to reduce reflected powerand improve efficiency is with a matching network.

[0033] Matching networks 32A and 32B match the output impedance ofgenerators 31A and 31B with their respective coils 29 and 30. The RFcontrol circuit may tune both matching networks by changing the value ofcapacitors within the matching networks to match the generator to theload as the load changes. The RF control circuit may tune a matchingnetwork when the power reflected from the load back to the generatorexceeds a certain limit. One way to provide a constant match, andeffectively disable the RF control circuit from tuning the matchingnetwork, is to set the reflected power limit above any expected value ofreflected power. This may help stabilize a plasma under some conditionsby holding the matching network constant at its most recent condition.Other measures may also help stabilize a plasma. For example, the RFcontrol circuit can be used to determine the power delivered to the load(plasma) and may increase or decrease the generator output power to keepthe delivered power substantially constant during deposition of a layer.

[0034] A gas delivery system 33 provides gases from several sources,34A-34F chamber for processing the substrate via gas delivery lines 38(only some of which are shown). As would be understood by a person ofskill in the art, the actual sources used for sources 34A-34F and theactual connection of delivery lines 38 to chamber 13 varies depending onthe deposition and cleaning processes executed within chamber 13. Gasesare introduced into chamber 13 through a gas ring 37 and/or a top nozzle45. FIG. 1B is a simplified, partial cross-sectional view of chamber 13showing additional details of gas ring 37.

[0035] In one embodiment, first and second gas sources, 34A and 34B, andfirst and second gas flow controllers, 35A′ and 35B′, provide gas toring plenum 36 in gas ring 37 via gas delivery lines 38 (only some ofwhich are shown). Gas ring 37 has a plurality of gas nozzles 39 (onlyone of which is shown for purposes of illustration) that provide auniform flow of gas over the substrate. Nozzle length and nozzle anglemay be changed to allow tailoring of the uniformity profile and gasutilization efficiency for a particular process within an individualchamber. In a preferred embodiment, gas ring 37 has 12 gas nozzles 39made from an aluminum oxide ceramic.

[0036] Gas ring 37 also has a plurality of gas nozzles 40 (only one ofwhich is shown), which in a preferred embodiment are co-planar with andshorter than source gas nozzles 39, and in one embodiment receive gasfrom body plenum 41. Gas nozzles 39 and 40 are not fluidly coupled insome embodiments it is desirable not to mix gases before injecting thegases into chamber 13. In other embodiments, gases may be mixed prior toinjecting the gases into chamber 13 by providing apertures (not shown)between body plenum 41 and gas ring plenum 36. In one embodiment, thirdand fourth gas sources, 34C and 34D, and third and fourth gas flowcontrollers, 35C and 35D′, provide gas to body plenum via gas deliverylines 38. Additional valves, such as 43B (other valves not shown), mayshut off gas from the flow controllers to the chamber.

[0037] In embodiments where flammable, toxic, or corrosive gases areused, it may be desirable to eliminate gas remaining in the gas deliverylines after a deposition. This may be accomplished using a 3-way valve,such as valve 43B, to isolate chamber 13 from delivery line 38A and tovent delivery line 38A to vacuum foreline 44, for example. As shown inFIG. 1A, other similar valves, such as 43A and 43C, may be incorporatedon other gas delivery lines. Such 3-way valves may be placed as close tochamber 13 as practical, to minimize the volume of the unvented gasdelivery line (between the 3-way valve and the chamber). Additionally,two-way (on-off) valves (not shown) may be placed between a mass flowcontroller (“MFC”) and the chamber or between a gas source and an MFC.

[0038] Referring again to FIG. 1A, chamber 13 also has top nozzle 45 andtop vent 46. Top nozzle 45 and top vent 46 allow independent control oftop and side flows of the gases, which improves film uniformity andallows fine adjustment of the film's deposition and doping parameters.Top vent 46 is an annular opening around top nozzle 45. In oneembodiment, first gas source 34A supplies source gas nozzles 39 and topnozzle 45. Source nozzle MFC 35A′ controls the amount of gas deliveredto source gas nozzles 39 and top nozzle MFC 35A controls the amount ofgas delivered to top gas nozzle 45. Similarly, two MFCs 35B and 35B′ maybe used to control the flow of oxygen to both top vent 46 and oxidizergas nozzles 40 from a single source of oxygen, such as source 34B. Thegases supplied to top nozzle 45 and top vent 46 may be kept separateprior to flowing the gases into chamber 13, or the gases may be mixed intop plenum 48 before they flow into chamber 13. Separate sources of thesame gas may be used to supply various portions of the chamber.

[0039] A remote microwave-generated plasma cleaning system 50 isprovided to periodically clean deposition residues from chambercomponents. The cleaning system includes a remote microwave generator 51that creates a plasma from a cleaning gas source 34E (e.g., molecularfluorine, nitrogen trifluoride, other fluorocarbons or equivalents) inreactor cavity 53. The reactive species resulting from this plasma areconveyed to chamber 13 through cleaning gas feed port 54 via applicatortube 55. The materials used to contain the cleaning plasma (e.g., cavity53 and applicator tube 55) must be resistant to attack by the plasma.The distance between reactor cavity 53 and feed port 54 should be keptas short as practical, since the concentration of desirable plasmaspecies may decline with distance from reactor cavity 53. Generating thecleaning plasma in a remote cavity allows the use of an efficientmicrowave generator and does not subject chamber components to thetemperature, radiation, or bombardment of the glow discharge that may bepresent in a plasma formed in situ. Consequently, relatively sensitivecomponents, such as electrostatic chuck 20, do not need to be coveredwith a dummy wafer or otherwise protected, as may be required with an insitu plasma cleaning process.

[0040] System controller 60 controls the operation of system 10. In apreferred embodiment, controller 60 includes a memory 62, such as a harddisk drive, a floppy disk drive (not shown), and a card rack (not shown)coupled to a processor 61. The card rack may contain a single-boardcomputer (SBC) (not shown), analog and digital input/output boards (notshown), interface boards (not shown), and stepper motor controllerboards (not shown). The system controller conforms to the Versa ModularEuropean (VME) standard, which defines board, card cage, and connectordimensions and types. The VME standard also defines the bus structure ashaving a 16-bit data bus and 24-bit address bus. System controller 60operates under the control of a computer program stored on the hard diskdrive or through other computer programs, such as programs stored on aremovable disk. The computer program dictates, for example, the timing,mixture of gases, RF power levels and other parameters of a particularprocess. The interface between a user and the system controller is via amonitor, such as a cathode ray tube (CRT) 65, and a light pen 66, asdepicted in FIG. 1C.

[0041]FIG. 1C is an illustration of a portion of an exemplary systemuser interface used in conjunction with the exemplary CVD processingchamber of FIG. 1A. System controller 60 includes a processor 61 coupledto a computer-readable memory 62. Preferably, memory 62 may be a harddisk drive, but memory 62 may be other kinds of memory, such as ROM,PROM, and others.

[0042] System controller 60 operates under the control of a computerprogram 63 stored in a computer-readable format within memory 62. Thecomputer program dictates the timing, temperatures, gas flows, RF powerlevels and other parameters of a particular process. The interfacebetween a user and the system controller is via a CRT monitor 65 and alight pen 66, as depicted in FIG. 1C. In a preferred embodiment, twomonitors, 65 and 65A, and two light pens, 66 and 66A, are used, onemounted in the clean room wall (65) for the operators and the otherbehind the wall (65A) for the service technicians. Both monitorssimultaneously display the same information, but only one light pen(e.g. 66) is enabled. To select a particular screen or function, theoperator touches an area of the display screen and pushes a button (notshown) on the pen. The touched area confirms being selected by the lightpen by changing its color or displaying a new menu, for example.

[0043] The computer program code can be written in any conventionalcomputer-readable programming language such as 68000 assembly language,C, C++, or Pascal. Suitable program code is entered into a single file,or multiple files, using a conventional text editor and is stored orembodied in a computer-usable medium, such as a memory system of thecomputer. If the entered code text is in a high level language, the codeis compiled, and the resultant compiler code is then linked with anobject code of precompiled windows library routines. To execute thelinked compiled object code, the system user invokes the object codecausing the computer system to load the code in memory. The CPU readsthe code from memory and executes the code to perform the tasksidentified in the program.

[0044]FIG. 1D shows an illustrative block diagram of the hierarchicalcontrol structure of computer program 100. A user enters a process setnumber and process chamber number into a process selector subroutine 110in response to menus or screens displayed on the CRT monitor by usingthe light pen interface. The process sets are predetermined sets ofprocess parameters necessary to carry out specified processes, and areidentified by predefined set numbers. Process selector subroutine 110identifies (i) the desired process chamber in a multichamber system, and(ii) the desired set of process parameters needed to operate the processchamber for performing the desired process. The process parameters forperforming a specific process relate to conditions such as process gascomposition and flow rates, temperature, pressure, plasma conditionssuch as RF power levels, and chamber dome temperature, and are providedto the user in the form of a recipe. The parameters specified by therecipe are entered utilizing the light pen/CRT monitor interface.

[0045] The signals for monitoring the process are provided by the analogand digital input boards of system controller 60, and the signals forcontrolling the process are output on the analog and digital outputboards of system controller 60. A process sequencer subroutine 120comprises program code for accepting the identified process chamber andset of process parameters from the process selector subroutine 110 andfor controlling operation of the various process chambers. Multipleusers can enter process set numbers and process chamber numbers, or asingle user can enter multiple process set numbers and process chambernumbers; sequencer subroutine 120 schedules the selected processes inthe desired sequence. Preferably, sequencer subroutine 120 includes aprogram code to perform the steps of (i) monitoring the operation of theprocess chambers to determine if the chambers are being used, (ii)determining what processes are being carried out in the chambers beingused, and (iii) executing the desired process based on availability of aprocess chamber and type of process to be carried out. Conventionalmethods of monitoring the process chambers can be used, such as polling.When scheduling which process is to be executed, sequencer subroutine120 can be designed to take into consideration the “age of eachparticular user-entered request, or the present condition of the processchamber being used in comparison with the desired process conditions fora selected process, or any other relevant factor a system programmerdesires to include for determining scheduling priorities.

[0046] After sequencer subroutine 120 determines which process chamberand process set combination is going to be executed next, sequencersubroutine 120 initiates execution of the process set by passing theparticular process set parameters to a chamber manager subroutine130A-C, which controls multiple processing tasks in chamber 13 andpossibly other chambers (not shown) according to the process set sent bysequencer subroutine 120.

[0047] Examples of chamber component subroutines are substratepositioning subroutine 140, process gas control subroutine 150, pressurecontrol subroutine 160, and plasma control subroutine 170. Those havingordinary skill in the art will recognize that other chamber controlsubroutines can be included depending on what processes are selected tobe performed in chamber 13. In operation, chamber manager subroutine130A selectively schedules or calls the process component subroutines inaccordance with the particular process set being executed. Chambermanager subroutine 130A schedules process component subroutines in thesame manner that sequencer subroutine 120 schedules the process chamberand process set to execute. Typically, chamber manager subroutine 130Aincludes steps of monitoring the various chamber components, determiningwhich components need to be operated based on the process parameters forthe process set to be executed, and causing execution of a chambercomponent subroutine responsive to the monitoring and determining steps.

[0048] Operation of particular chamber component subroutines will now bedescribed with reference to FIGS. 1A and 1D. Substrate positioningsubroutine 140 comprises program code for controlling chamber componentsthat are used to load a substrate onto substrate support number 18.Substrate positioning subroutine 140 may also control transfer of asubstrate into chamber 13 from, e.g., a PECVD reactor or other reactorin the multi-chamber system, after other processing has been completed.

[0049] Process gas control subroutine 150 has program code forcontrolling process gas composition and flow rates. Subroutine 150controls the open/close position of the safety shut-off valves and alsoramps up/ramps down the mass flow controllers to obtain the desired gasflow rates. All chamber component subroutines, including process gascontrol subroutine 150, are invoked by chamber manager subroutine 130A.Subroutine 150 receives process parameters from chamber managersubroutine 130A related to the desired gas flow rates.

[0050] Typically, process gas control subroutine 150 opens the gassupply lines, and repeatedly (i) reads the necessary mass flowcontrollers, (ii) compares the readings to the desired flow ratesreceived from chamber manager subroutine 130A, and (iii) adjusts theflow rates of the gas supply lines as necessary. Furthermore, processgas control subroutine 150 may include steps for monitoring the gas flowrates for unsafe rates and for activating the safety shut-off valveswhen an unsafe condition is detected.

[0051] In some processes, an inert gas, such as argon, is flowed intochamber 13 to stabilize the pressure in the chamber before reactiveprocess gases are introduced. For these processes, the process gascontrol subroutine 150 is programmed to include steps for flowing theinert gas into chamber 13 for an amount of time necessary to stabilizethe pressure in the chamber. The steps described above may then becarried out.

[0052] Additionally, when a process gas is to be vaporized from a liquidprecursor, for example, tetraethylorthosilane (TEOS), the process gascontrol subroutine 150 may include steps for bubbling a delivery gassuch as helium through the liquid precursor in a bubbler assembly or forintroducing the helium to a liquid injection valve. For this type ofprocess, the process gas control subroutine 150 regulates the flow ofthe delivery gas, the pressure in the bubbler, and the bubblertemperature to obtain the desired process gas flow rates. As discussedabove, the desired process gas flow rates are transferred to process gascontrol subroutine 150 as process parameters.

[0053] Furthermore, the process gas control subroutine 150 includessteps for obtaining the necessary delivery gas flow rate, bubblerpressure, and bubbler temperature for the desired process gas flow rateby accessing a stored table containing the necessary values for a givenprocess gas flow rate. Once the necessary values are obtained, thedelivery gas flow rate, bubbler pressure and bubbler temperature aremonitored, compared to the necessary values and adjusted accordingly.

[0054] The process gas control subroutine 150 may also control the flowof heat-transfer gas, such as helium (He), through the inner and outerpassages in the wafer chuck with an independent helium control (IHC)subroutine (not shown). The gas flow thermally couples the substrate tothe chuck. In a typical process, the wafer is heated by the plasma andthe chemical reactions that form the layer, and the He cools thesubstrate through the chuck, which may be water-cooled. This keeps thesubstrate below a temperature that may damage preexisting features onthe substrate.

[0055] Pressure control subroutine 160 includes program code forcontrolling the pressure in chamber 13 by regulating the size of theopening of throttle valve 26 in the exhaust portion of the chamber.There are at least two basic methods of controlling the chamber with thethrottle valve. The first method relies on characterizing the chamberpressure as it relates to, among other things, the total process gasflow, the size of the process chamber, and the pumping capacity. Thefirst method sets throttle valve 26 to a fixed position. Settingthrottle valve 26 to a fixed position may eventually result in asteady-state pressure.

[0056] Alternatively, the chamber pressure may be measured, with amanometer for example, and the position of throttle valve 26 may beadjusted according to pressure control subroutine 160, assuming thecontrol point is within the boundaries set by gas flows and exhaustcapacity. The former method may result in quicker chamber pressurechanges, as the measurements, comparisons, and calculations associatedwith the latter method are not invoked. The former method may bedesirable where precise control of the chamber pressure is not required,whereas the latter method may be desirable where an accurate,repeatable, and stable pressure is desired, such as during thedeposition of a layer.

[0057] When pressure control subroutine 160 is invoked, the desired, ortarget, pressure level is received as a parameter from chamber managersubroutine 130A. Pressure control subroutine 160 measures the pressurein chamber 13 by reading one or more conventional pressure manometersconnected to the chamber; compares the measured value(s) to the targetpressure; obtains proportional, integral, and differential (PID) valuesfrom a stored pressure table corresponding to the target pressure, andadjusts throttle valve 26 according to the PID values obtained from thepressure table. Alternatively, pressure control subroutine 160 may openor close throttle valve 26 to a particular opening size to regulate thepressure in chamber 13 to a desired pressure or pressure range.

[0058] Plasma control subroutine 170 comprises program code forcontrolling the frequency and power output setting of RF generators 31Aand 31B and for tuning matching networks 32A and 32B. Plasma controlsubroutine 170, like the previously described chamber componentsubroutines, is invoked by chamber manager subroutine 130A.

[0059] An example of a system that may incorporate some or all of thesubsystems and routines described above would be the ULTIMA™ system,manufactured by APPLIED MATERIALS, INC., of Santa Clara, Calif.,configured to practice the present invention. Further details of such asystem are disclosed in U.S. Pat. No. 6,170,428, issued Jan. 9, 2001,entitled “Symmetric Tunable Inductively-Coupled HDP-CVD Reactor,” havingFred C. Redeker, Farhad Moghadam, Hirogi Hanawa, Tetsuya Ishikawa, DanMaydan, Shijian Li, Brian Lue, Robert Steger, Yaxin Wang, Manus Wong andAshok Sinha listed as co-inventors, the disclosure of which isincorporated herein by reference. The described system is for exemplarypurpose only. It would be a matter of routine skill for a person ofskill in the art to select an appropriate conventional substrateprocessing system and computer control system to implement the presentinvention.

[0060] III. Depositing a Silicon Oxide Film According to SpecificEmbodiments of the Invention

[0061] As previously stated, embodiments of the present invention can bepracticed in an HDP-CVD chamber such as exemplary chamber 13 describedabove. FIG. 2 illustrates one particular embodiment of the invention asused to deposit a silicon oxide film over a semiconductor substrate. Theprocess is for exemplary purposes and is not intended to limit the scopeof the claims of the present invention. Where applicable, referencenumbers in the description below are used to refer to appropriatecomponents of the exemplary chamber of FIGS. 1A-1D. In this embodimentthe process is implemented and controlled using a computer programstored in the memory 62 of system controller 60.

[0062] The method shown in FIG. 2 deposits an undoped silicon oxidelayer by flowing a process gas into chamber 13 (step 200) and forming aplasma from the process gas (step 205). The length of the depositionprocess is determined by the desired thickness of the silicon oxidefilm.

[0063] One manner in which the deposition process shown in FIG. 2differs from previous HDP-CVD silicon oxide deposition processes is byadding a flow of a hydrogen-containing source to the traditional siliconoxide deposition gas. As is known to those of skill in the art, anHCP-CVD silicon oxide film is generally deposited from a process gasthat includes a silane gas (e.g., SiH₄, Si₂H₆, etc.), anoxygen-containing source (e.g., O₂) and an inert gas (e.g., Ar).Generally, deposition conditions for such a silicon oxide film arecarefully controlled in order to minimize the amount of hydrogenincorporated into the film because as is known to those of skill in theart, hydrogen is a source of film instability. The inventors haveunexpectedly discovered, however, that adding a flow of ahydrogen-containing gas in step 200 can increase the gap-fill capabilityof the film without leading to film instability provided otherdeposition conditions are maintained within certain ranges as describedin more detail below. In various embodiments, the hydrogen-containinggas can be one or more of the following: molecular hydrogen (H₂), water(H₂O), ammonia (NH₃), methane (CH₄), ethane (C₂H₆) or another hydridegas that does not include silicon, boron or phosphorus. Using a hydridethat includes boron or phosphorus (e.g., PH₃ or B₂H₆) would result inthe inclusion of boron or phosphorus, respectively, in the film and thusproduce a BSG or PSG film as opposed to a USG film. In one particularembodiment, the process gas consists of SiH₄, O₂, Ar and H₂.

[0064] In order to better appreciate the benefits achievable by thehydrogen-assisted silicon oxide deposition process shown in FIG. 2 it isuseful to first understand some of the problems associated with a wellknown previously used HDP-CVD silicon oxide deposition process. Thiswell known process deposits an undoped silicon oxide film from a processgas of SiH₄, O₂ and Ar and can be implemented in the exemplary chamberdescribed above. One specific process that has been recommended in thepast for PMD gap-fill applications employs the deposition conditionsshown below in Table 1. TABLE 1 PREVIOUSLY KNOWN HDP-CVD SiO₂ DEPOSITIONPROCESS Parameter Value SiH₄ flow 60 + 11 sccm O₂ flow 140 sccm Ar flow80 + 12 sccm Pressure 2-4 mTorr (TVO) Temperature 550° C. Top RF Power4900 Watts Side RF Power 3000 Watts Bias RF Power 2000 Watts

[0065] For the gas flow entries within table 1 that include two numbers,the first number indicates the flow rate of the particular gas throughside nozzles 39, 40 while the second number indicates the flow rate ofthe gas through top nozzle 45. Also, TVO means “throttle valve fullyopen” which results in chamber pressure being controlled by the quantityof gas flowed into the chamber.

[0066] FIGS. 3A-3C, which are simplified cross-sectional views of asilicon oxide film at different stages of deposition, illustrate thepotential gap-fill limitation that is associated with the process recipeof Table 1 for certain small width gaps having relatively high aspectratios. It is important to understand that while HDP-CVD silicon oxidedeposition techniques generally provide for improved gap-fill ascompared to other plasma silicon oxide deposition techniques includinglow density, capacitively coupled plasma CVD techniques, the gap-fillissues associated with those techniques become an issue for HDP-CVDtechniques in certain aggressive gap-fill applications, for example,gaps having a width of 0.1 μm and a 5:1 aspect ratio. The gap-fillproblem illustrated in FIGS. 3A-3C is somewhat exaggerated in order tobetter illustrate the problem.

[0067]FIG. 3A shows the initial stages of film deposition over asubstrate (not shown) having a gap 220 defined by two adjacent features222, 224 formed over the substrate. As shown in FIG. 3A, theconventional HDP-CVD silicon oxide deposition process results in directsilicon oxide deposition on horizontal surface 226 within gap 220 andhorizontal surfaces 228 above features 222, 224. The process alsoresults in indirect deposition (referred to as re-deposition) of siliconoxide on sidewalls 230 due to the recombination of material sputteredfrom the silicon oxide film as it grows. In certain small-width,high-aspect-ratio applications, the continued growth of the siliconoxide film results in formations 232 on the upper section gap sidewallthat grow toward each other at a rate of growth exceeding the rate atwhich the film grows laterally on lower portions 234 of the sidewall(see FIG. 3B also). The final result of this process is that a void 236forms as shown in FIG. 3C.

[0068] The deposition process discussed with respect to FIG. 2 hasimproved gap-fill capabilities as compared to those of the conventionalfilm outlined in Table 1. FIGS. 4A-4C illustrate how a film depositedaccording to the process of FIG. 2 is able to completely fill a gap 240where the film of Table 1 was not capable of filling the gap in avoid-free manner. Each of FIGS. 4A-4C represents growth of the siliconoxide film deposited according to FIG. 2 at the same point in thedeposition process as the corresponding one of FIGS. 3A-3C. For example,each of FIGS. 3A and 4A may represent film growth after 10 seconds. Itis important to note, however, that none of FIGS. 3A-3C or 4A-4C areintended to be drawn to scale and the actual aspect ratio of the gapsrepresented in these figures is higher than it appears to be ifmeasuring the figures.

[0069] As shown in FIG. 4A, an HDP-CVD silicon oxide film depositedaccording to the process of FIG. 2 grows on a horizontal surface 244within gap 240 at approximately the same rate as the film discussed withrespect to FIG. 3A. Film growth on horizontal surfaces 246 on top offeature 242, however, is slower than film growth on surfaces 228 in FIG.3A. Similarly, film growth or re-deposition on an upper portion 248 ofthe gap sidewall is slower than in FIG. 3A.

[0070] As shown in FIGS. 4B and 4C, these differences in film growthrate result in a more even growth within small-width, high aspect ratiogap 240 without the tendency to form an undesirable void within the gap.While not being limited to any particular theory, it is believed thatthe process of FIG. 2 achieves superior gap-fill results becausedeposition conditions result in excessive hydrogen cations (H⁺) on thesurface of the sidewall. These excessive hydrogen cations take the placeof some silane cations (SiH_(x) ⁺) on the surface of the sidewall andreadily react with oxygen anions (O⁻) to form volatile H₂O that ispumped out of the chamber. This reaction reduces the amount of Osputtering, which in turn reduces SiO₂ deposition on the sidewallbecause sidewall deposition, especially for trenches with a verticalsidewall, is largely initiated by sputter re-deposition. Thus, less SiO₂is deposited on the sidewall than in processes that do not employ thetechniques of the present invention.

[0071] The inventors have found that in order to deposit ahydrogen-assisted HDP-CVD silicon oxide film so that the deposited filmdoes not include increased levels of hydrogen which could lead to filminstability the ratio of the flow rate of the oxygen-containing sourceto the combined flow rate of the silane gas and hydrogen-containing gasin some embodiments should be between 1.6 and 2.5 to 1 inclusive. Atratios below 1.6:1 the silicon oxide film becomes silicon rich, exhibitspoor electrical breakdown characteristics and has an undesirably highrefractive index. At ratios above 1.6:1, the relatively high gas flowrates required to achieve such ratios increases the chamber pressure toundesirably high levels which in turn degrades film gapfillcapabilities.

[0072] Also, the ratio of the flow rate of the hydrogen-containing gasto the silane gas in some embodiments should be between 0.5-2.0:1inclusive. At ratios below 0.5:1, not enough additional hydrogen isintroduced to achieve desirable gapfill benefits, and at ratios higherthan 2.0:1, the relatively high gas flow rates required to achieve suchratios increases the chamber pressure to undesirably high levels whichin turn degrades film gapfill capabilities.

[0073] The method of the present invention is particularly useful forthe deposition of undoped silicon oxide layers for PMD and STIapplications. Each of these applications often involve gapfillrequirements that are more aggressive, i.e., higher aspect ratio gaps,than IMD applications. Thus, the deposition process of many embodimentsof the invention occurs at a substrate temperature above 450° C. andmore typically between 500° C. and 750° C. Films deposited according tothese embodiments generally have a hydrogen content, as measured byAuger analysis, of between 1.5-1.6 atomic percent. This is comparable toabout 1.5 at. % hydrogen content of a standard HDP-CVD USG filmdeposited from a process gas of SiH₄, O₂ and Ar using the parameters ofTable 1.

[0074] A comparison of FIGS. 6A and 6B to FIGS. 5A and 5B illustratesthe benefits of a deposition process according to FIG. 2 as compared toa process according to Table 1. FIGS. 5A and 5B are a simplifiedcross-sectional view of a silicon oxide film deposited according to theprocess of Table 1. In FIG. 5A, the film is deposited over a substratehaving multiple sets of raised features defining 0.15 μm wide gaps 260and 0.17 μm wide gaps 262. The height of gaps 260 and 262 is 0.7 μm sothe aspect ratio of gaps 260 is approximately 4.7:1 while the aspectratio of gaps 262 is approximately 4.1:1. As evident from FIG. 5A, thesilicon oxide film is not able to completely fill gaps 260 without theformation of voids 264 within the gaps. Similarly, while no voids areformed within gaps 262, the deposition process results in a surfacetopology that includes unfilled areas 266 near the upper strata of gap262.

[0075] In contrast, FIG. 6A shows deposition of an HDP-CVD silicon oxidefilm according to the process of FIG. 2 over 0.15 μm and 0.17 μm gaps270 and 272 having aspect ratios identical to the respective gaps inFIG. 5A. As evident from FIG. 6A, the film deposited according to theprocess of FIG. 2 has superior gap-fill capabilities as compared to thefilm of FIG. 5A. Gaps 272 are completely filled without voids and voids274 within gaps 270 are smaller than voids 264 within gaps 260. Furtherevidence of the superiority of the process of FIG. 2 as compared to thatof Table 1 is evident from a comparison of FIG. 6B to FIG. 5B. Thesubstrates shown in FIGS. 5B and 6B include trenches 280 having a widthsof 0.1 μm at the top of the trench and a width as low as 0.02 μm at thebottom of the trench. The midpoint 282 of trenches 280 has a width ofabout 0.05 μm and the height of the trenches is 0.4 μm. Using the widthof the trench at midpoint 282 to calculate its aspect ratios, as iscommonly done, the aspect ratio of trenches 280 is 8.0:1. As evidentfrom the figures, however, the film deposited according to the processof FIG. 2 (FIG. 6B) does not include any voids within the gaps and thushas superior gap-fill capabilities as compared to the film depositedaccording to the process of Table 1 (FIG. 5B).

[0076] The process parameters set forth above with respect to theembodiments above are optimized for particular deposition processes runin an Ultima HDP chamber manufactured by Applied Materials that isoutfitted for 200 mm wafers. A person of ordinary skill in the art willrecognize that these preferred parameters are in part chamber specificand will vary if chambers of other design and/or volume are employed.

[0077] The parameters listed in the above preferred processes and theabove-described experiments should not be limiting to the claims asdescribed herein. One of ordinary skill in the art can also useparameters and conditions other than those described with respect tospecific embodiments. As such, the above description is illustrative andnot restrictive. The scope of the invention should, therefore, bedetermined not with reference to the above description, but insteadshould be determined with reference to the appended claims along withtheir full scope of equivalents.

What is claimed is:
 1. A substrate processing apparatus comprising: asubstrate processing chamber; a gas distribution system operativelycoupled to said chamber; a high density plasma power source; acontroller operatively coupled to said gas distribution system and saidhigh density plasma power source; a memory coupled to said controller,said memory including computer instructions embodied in acomputer-readable format, said computer instructions comprising:instructions that control said gas distribution system to flow a processgas into the substrate processing chamber, the process gas comprising asilane gas, an oxygen-containing source, an inert gas and ahydrogen-containing source that is either molecular hydrogen or ahydride gas that does not include silicon, boron or phosphorus; andinstructions that control said high density plasma source to form aplasma having an ion density of at least 1×10¹¹ ions/cm³ from saidprocess gas to deposit said silicon oxide layer over said substrate. 2.The apparatus of claim 1 wherein said hydride gas is selected from thegroup of H₂O, NH₃, CH₄ and C₂H₆.
 3. The apparatus of claim 1 whereinsaid silane gas is SiH₄.
 4. The apparatus of claim 3 wherein saidoxygen-containing source is O₂.
 5. The apparatus of claim 3 wherein saidinert gas comprises argon.
 6. The apparatus of claim 1 wherein saiddeposited silicon oxide film contains less than or equal to 2 atomicpercent hydrogen
 7. The apparatus of claim 1 wherein said instructionsthat control said gas distribution system flow gases such that a flowratio of said oxygen containing source to said silane gas combined withsaid hydrogen containing source is between 1.6 and 2.5:1 inclusive. 8.The apparatus of claim 1 wherein said instructions that control said gasdistribution system flow gases such that a flow ratio of said hydrogencontaining source to said silane gas is between 0.5 2.0:1 inclusive. 9.The apparatus of claim 1 wherein the instructions that control said highdensity plasma source control said high density plasma source in amanner that results in said substrate being heated to a temperatureabove 450° C. during deposition of said silicon oxide layer.
 10. Asubstrate processing apparatus comprising: a substrate processingchamber; a gas distribution system operatively coupled to said chamber;a high density plasma power source; a controller operatively coupled tosaid gas distribution system and said high density plasma power source;a memory coupled to said controller, said memory including computerinstructions embodied in a computer-readable format, said computerinstructions comprising: instructions that control said gas distributionsystem to flow a process gas into the substrate processing chamber, theprocess gas comprising SiH₄, O₂, Ar and a hydrogen containing sourcecomprising one or more of H₂, H₂O, NH₃, CH₄ and C₂H₆ into the substrateprocessing chamber; and instructions that control said high densityplasma source to form a plasma having an ion density of at least 1×10¹¹ions/cm³ from said process gas to deposit said silicon oxide layer oversaid substrate.
 11. The apparatus of claim 10 wherein said hydrogencontaining source is H₂.